Graft-versus-host disease after allogeneic hematopoietic stem cell transplantation induces a CD8+ T cell-mediated graft-versus-tumor effect that is independent of the recognition of alloantigenic tumor targets

Comparison of antibody-based immunotherapeutics for malignant hematological disease in an experimental murine model

ABSTRACT

Antibody-based immunotherapies have revolutionized leukemia and lymphoma treatment, with animal studies being crucial in evaluating effectiveness and side effects. By targeting the evolutionary conserved Slamf7 immune receptor, which is naturally expressed by the murine multiple myeloma cell line MPC-11, we have developed a syngeneic mouse model for direct comparison of 3 immunotherapies: monoclonal antibodies (mAb), bispecific T-cell engagers (BiTE), and chimeric antigen receptor (CAR) T cells (CART), all targeting Slamf7. Slamf7-BiTE is a bispecific single-chain antibody consisting of α-Slamf7 and α-CD3 Fv fragments joined through a Gly-Ser linker, and Slamf7-CART comprises the α-Slamf7 Fv fragment fused to the msCD8α transmembrane and msCD28, 4-1BB, and CD3ζ intracellular signaling domains. Slamf7-BiTE and Slamf7-CART effectively killed MPC-11 cells in vitro, independently of Slamf7-mediated inhibitory signaling by self-ligation. After chimerizing the constant region of the rat-anti-mouse Slamf7 antibody to mouse Fc-immunoglobulin G2a for enhanced effector functions, Slamf7-mAb triggered antigen-specific antibody-dependent cellular cytotoxicity by binding to Fcγ receptor IV. In vivo, all 3 immunotherapies showed antitumor effects against Slamf7-expressing targets. Unlike Slamf7-mAb, Slamf7-BiTE led to considerable side effects in test animals, including weight loss and general malaise, which were also observed to a lesser extent after Slamf7-CART infusion. In allogeneic transplant, Slamf7-BiTE and Slamf7-CART maintained activity compared with the nontransplant setting, whereas Slamf7-mAb displayed enhanced antimyeloma activity. In summary, our model faithfully replicates treatment efficacy and side effects detected after human immunotherapy. It aids in developing and improving immunotherapies and may help devise novel approaches to mitigate undesired effects in steady state and allogeneic stem cell transplantation.

Immunotherapy for neuroblastoma by hematopoietic cell transplantation and post-transplant immunomodulation

Neuroblastoma represents a relatively common childhood tumor that imposes therapeutic difficulties. High risk neuroblastoma patients have poor prognosis, display limited response to radiochemotherapy and may be treated by hematopoietic cell transplantation. Allogeneic and haploidentical transplants have the distinct advantage of reinstitution of immune surveillance, reinforced by antigenic barriers. The key factors favorable to ignition of potent anti-tumor reactions are transition to adaptive immunity, recovery from lymphopenia and removal of inhibitory signals that inactivate immune cells at the local and systemic levels. Post-transplant immunomodulation may further foster anti-tumor reactivity, with positive but transient impact of infusions of lymphocytes and natural killer cells both from the donor, the recipient or third party. The most promising approaches include introduction of antigen-presenting cells in early post-transplant stages and neutralization of inhibitory signals. Further studies will likely shed light on the nature and actions of suppressor factors within tumor stroma and at the systemic level.

Mesenchymal stem cells in the fight against viruses: Face to face with the invisible enemy

The relative ease of isolation of mesenchymal stem cells (MSCs) from different tissues coupled with their culture expansion in vitro and their differentiation capacity to mesodermal, endodermal and ectodermal lineages have made these cells attractive for a large number of therapeutic applications. In recent years, there has been remarkable progress in the utilization of MSCs in diverse clinical indications both in animal models and human clinical trials. However, the potential of MSCs to control or treat viral diseases is still in its infancy. In this study, we report quantitative data on the MSC-based clinical trials over the last ten years as they appear on the online database of clinical research studies from US National Institutes of Health. In particular, we provide comprehensive review of either completed or ongoing clinical trials using MSCs for virus-associated diseases focusing on HIV, hepatitis B virus and COVID-19 virus.

Allogeneic dendritic cells induce potent antitumor immunity by activating KLRG1+CD8 T cells

The graft-versus-leukemia effect reminds us to observe the allogeneic cell elicited anti-tumor immune responses. Here we immunized recipient B6 mice with different types of allogenic leukocytes and found that vaccination with allogenic dendritic cells (alloDC) elicited the most efficient protection against broad-spectrum tumors. The recipient lymphocytes were analyzed and the data showed that CD8 T cells increased significantly after immunization and expressed effector memory T cell marker KLRG1. Functional evaluation demonstrated that these KLRG1⁺CD8 T cells could kill tumor cells in vitro and in vivo in Granzyme B- and Fas/FasL-dependent manners with no tumor antigen specificity, and tend to migrate into tumor sites by high expression of heparanase. Adoptive transfer of these cells could provide antitumor protection against tumors. AlloDC could also treat mice with residual tumors and combination of anti-PD1 antibody could enhance this effects. Together, our study showed that alloDC-immunization could induce potent antitumor effect through the expansion of KLRG1⁺CD8 T cells, which can work as both preventive and therapeutic tumor vaccines.

Alloantigen expression on malignant cells and healthy host tissue influences graft-versus-tumor reactions after allogeneic hematopoietic stem cell transplantation

Durable remissions of hematological malignancies regularly observed following allogeneic hematopoietic stem cell transplantation (aHSCT) are due to the conditioning regimen, as well as an immunological phenomenon called graft-versus-leukemia (GVL) or graft-versus-tumor (GVT) effect. The development of GVL is closely linked to graft-versus-host disease (GVHD), the main side effect associated with aHSCT. Both, GVHD and GVL are mediated by donor T cells that are initially activated by antigen-presenting cells that present recipient-derived alloantigens in the context of either matched or mismatched MHC class I molecules. Using murine models of aHSCT we show that ubiquitously expressed minor histocompatibility alloantigens (mHAg) are no relevant target for GVT effects. Interestingly, certain ubiquitously expressed MHC alloantigens augmented GVT effects early after transplantation, while others did not. The magnitude of GVT effects correlated with tumor infiltration by CD8+ cytotoxic T cells and tumor cell apoptosis. Furthermore, the immune response underlying GVHD and GVT was oligoclonal, highlighting that immunodominance is an important factor during alloimmune responses. These results emphasize that alloantigen expression on non-hematopoietic tissues can influence GVT effects in a previously unrecognized fashion. These findings bear significance for harnessing optimal GVL effects in patients receiving aHSCT.

Genetically engineered donor T cells to optimize graft-versus-tumor effects across MHC barriers

Hematopoietic stem cell transplantation has been used for more than 50 years to combat hematologic malignancies. In addition to being the first stem cell therapy, transplantation has provided evidence for the potent anti-tumor effects of T cells. Facilitating T-cell-based immunity against malignancies requires a careful balancing act between generating a robust response and avoiding off-target killing of healthy tissues, which is difficult to accomplish using bulk donor T cells. To address these issues, several approaches have been developed, drawing on basic T-cell biology, to potentiate graft-versus-tumor activity while avoiding graft-versus-host disease. Current strategies for anti-tumor cell therapies include: (i) selecting optimal T cells for transfer; (ii) engineering T cells to possess enhanced effector functions; and (iii) generating T-cell precursors that complete development after adoptive transfer. In this review, we assess the current state of the art in T-lineage cell therapy to treat malignancies in the context of allogeneic hematopoietic stem cell transplantation.

Multicenter analyses demonstrate significant clinical effects of minor histocompatibility antigens on GvHD and GvL after HLA-matched related and unrelated hematopoietic stem cell transplantation

The effect of minor H antigen mismatching on the occurrence of graft-versus-host disease (GvHD) and graft-versus-leukemia (GvL) after HLA-matched hematopoietic stem cell transplantation (HSCT) has mainly been demonstrated in single-center studies. Yet, the International Histocompatibility and Immunogenetics Workshops (IHIW) provide a collaborative platform to execute crucial large studies. In collaboration with 20 laboratories of the IHIW, the roles of 10 autosomal and 10 Y chromosome-encoded minor H antigens were investigated on GvHD and relapse incidence in 639 HLA-identical related donor (IRD) and 210 HLA-matched unrelated donor (MUD) HSCT recipients. Donor and recipient DNA samples were genotyped for the minor H antigens HA-1, HA-2, HA-3, HA-8, HB-1, ACC-1, ACC-2, SP110, PANE1, UGT2B17, and HY. The correlations with the primary outcomes GvHD (acute or chronic GvHD), survival, and relapse were statistically analyzed. The results of these multicenter analyses show that none of the HLA class I-restricted HY antigens were found to be associated with any of the primary outcomes. Interestingly, of the HLA class II-restricted HY antigens analyzed, HLA-DQ5 positive recipients showed a significantly increased GvHD-free survival in female-to-male HSCT compared with male-to-female HSCT (P = .013). Yet, analysis of the overall gender effect, thus independent of the known HY antigens, between the gender groups demonstrated an increased GvHD incidence in the female-to-male transplantations (P < .005) and a decreased GvHD-free survival in the female-to-male transplantations (P < .001). Of all autosomally encoded minor H antigens, only mismatching for the broadly expressed minor H antigen HA-8 increased the GvHD incidence in IRD HSCT (Hazard ratio [HR] = 5.28, P < .005), but not in MUD HSCT. Most striking was the influence of hematopoietic restricted minor H antigens on GvL as mismatching for hematopoietic minor H antigens correlated with lower relapse rates (P = .078), higher relapse-free survival (P = .029), and higher overall survival (P = .032) in recipients with GvHD, but not in those without GvHD. In conclusion, the significant GvHD effect of the broadly expressed minor H antigen HA-8 favors matching for HA-8 in IRD, but not in MUD, patient/donor pairs. The GvHD-GvL association demonstrating a significant lower relapse in hematopoietic minor H antigen mismatched patient/donor pairs underlines their clinical applicability for adoptive immunotherapy, enhancing the GvL effect in a GvHD controllable manner.

Emerging concepts in haematopoietic cell transplantation

Haematopoietic cell transplantation (HCT) is the most widely used form of cellular therapy. It is the only known cure for some haematological malignancies and has recently been used in additional clinical settings, such as allograft tolerance induction and treatment of autoimmune diseases. Recent advances have enabled HCT in a wider range of patients with improved outcomes. This Review summarizes the latest developments in this therapy, focusing on issues that will affect future advancement.

Donor CD4 T cells are critical in allogeneic stem cell transplantation against murine solid tumor

Nonmyeloablative allogeneic stem cell transplantation (SCT) has been used for various malignancies, although detailed mechanisms of antitumor effects remain unclear. We showed that a nonmyeloablative allogeneic SCT regimen, which consists of mixed chimerism induced by an injection of donor spleen and bone marrow cells followed by cyclophosphamide treatment and a donor lymphocyte infusion (DLI), exerted antitumor effects on established murine bladder tumor, MBT-2. An expansion of donor CD4 T cells accompanied by transient but vigorous IFN-gamma production was detected shortly after DLI. In vivo neutralization of IFN-gamma or depletion of CD4 T cells from DLI abolished the antitumor effects, indicating an indispensable role of donor CD4 T cells producing IFN-gamma. Donor as well as host CD8 T cells accumulated in the tumor region with time. Importantly, depletion of CD8 T cells from DLI did not reverse the suppression of tumor growth, indicating that CD4 T cells play a more essential role in mediating early antitumor effects. Furthermore, tumor-specific response of host CD8 T cells was suggested. These results not only provide the first evidence of nonmyeloablative allogeneic SCT for the treatment of bladder tumor but also elucidate detailed mechanisms of antitumor effects provoked by DLI.

Targeting a single mismatched minor histocompatibility antigen with tumor-restricted expression eradicates human solid tumors

Regressions of metastatic solid tumors after allogeneic human leukocyte antigen (HLA)–matched stem cell transplantation (SCT) are often associated with detrimental graft-versus-host disease (GVHD). The graft-versus-host reaction of the HLA-matched donor is directed mainly against the multiple mismatched minor histocompatibility antigens (mHags) of the patient. mHags are strong HLA-restricted alloantigens with differential tissue distribution. Ubiquitously expressed mHags are the prime in situ targets of GVHD. The mHag HA-1 is hematopoiesis restricted, but displays additionally an aberrant expression on solid tumors. Thus, HA-1 might be an excellent target to boost the anti–solid tumor effect of allogeneic SCT without inducing severe GVHD. Here, we show that cytotoxic T lymphocytes (CTLs) solely targeting the human mHag HA-1 are capable of eradicating 3-dimensional human solid tumors in a highly mHag-specific manner in vitro, accompanied by interferon-γ release. In vivo, HA-1–specific CTLs distribute systemically and prevent human breast cancer metastases in immunodeficient mice. Moreover, HA-1–specific CTLs infiltrate and inhibit the progression of fully established metastases. Our study provides the first proof for the efficacy of a clinically applicable concept to exploit single mismatched mHags with hematopoiesis- and solid tumor–restricted expression for boosting the anti–solid tumor effect of allogeneic SCT.

Clinical molecular imaging in intestinal graft-versus-host disease: mapping of disease activity, prediction, and monitoring of treatment efficiency by positron emission tomography

Gastrointestinal graft-versus-host disease (GVHD) is a common and potentially life-threatening complication after allogeneic hematopoietic stem-cell transplantation (HSCT). Noninvasive tests for assessment of GVHD activity are desirable but lacking. In the present study, we were able to visualize intestinal GVHD-associated inflammation in an allogeneic murine transplantation model by (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in vivo. A predominant localization of intestinal GVHD to the colon was verified by histology and fluorescence reflectance imaging of enhanced green fluorescent protein (EGFP)-expressing donor cells. Colonic infiltration by EGFP(+) donor lymphocytes matched increased FDG uptake in PET examinations. These preclinical data were prospectively translated into 30 patients with suspected intestinal GVHD beyond 20 days after transplantation. A total of 14 of 17 patients with a diagnostic histology showed significant FDG uptake of the gut, again predominantly in the colon. No increased FDG uptake was detected in 13 patients without histologic evidence of intestinal GVHD. Our findings indicate that FDG-PET is a sensitive and specific noninvasive imaging technique to assess intestinal GVHD, map its localization, and predict and monitor treatment responsiveness. Novel targeted tracers for PET may provide new insights into the pathophysiology of GVHD and bear the potential to further improve GVHD diagnosis.

Alloantigen recognition is critical for CD8 T cell-mediated graft anti-tumor activity against murine BCL1 lymphoma after myeloablative bone marrow transplantation

The goal of the current study was to determine whether whole bone marrow cells or splenic CD8(+) T cells from C57BL/6 (H-2(b)) donor mice, which are tolerant to BALB/c (H-2(d)) alloantigens, are capable of mediating graft anti-tumor activity against a BALB/c B-cell lymphoma after injection into irradiated BALB/c hosts. The experimental results show that high doses of splenic CD8(+) T cells mixed with T cell-depleted bone marrow cells from C57BL/6 non-tolerant (normal) donors eliminate the BCL(1) B-cell lymphoma cells and induce lethal graft-versus-host disease (GVHD). CD8(+) T cells from tolerant donors simultaneously lose both their ability to induce GVHD and their anti-tumor activity. Whole bone marrow cell transplants from normal donors eliminated BCL(1) tumor cells without inducing GVHD, and bone marrow cells from tolerant donors failed to eliminate the tumor cells. The infused BCL(1) tumor cells expressed an immunogenic tumor-specific idiotype antigen disparate from host alloantigens, indicating that recognition of the tumor-specific antigen alone was insufficient to elicit graft anti-tumor activity from unimmunized allotolerant donor splenic CD8(+) T cells or whole bone marrow cells. We conclude that CD8(+) T cells from unimmunized normal donor mice require alloantigen recognition to mediate their anti-tumor activity following allogeneic BMT.

Differential Requirement for a Cellular Type-1 Immune Response in Tumor-Associated Versus Alloantigen-Targeted GvT Effects

BACKGROUND

The major obstacles that impair successful outcome after allogeneic hematopoietic stem cell transplantation (HSCT) for hematologic malignancies remain graft-versus-host disease (GvHD) and tumor relapse. Improved survival after allogeneic HSCT therefore requires more effective control of GvHD while preserving graft-versus-tumor (GvT) effects.

METHODS

Allogeneic parent-into-F1 murine transplant models (BALB/c or C57BL/6 --> F1[BALB/cxC57BL/6]) were used to evaluate the interrelation of GvHD and GvT effects targeting tumor-specific antigens or alloantigens on MethA tumor cells.

RESULTS

Compared with syngeneic F1-into-F1 controls (F1[H-2(b/d)] --> F1: MethA[H-2d]), significant T cell-mediated GvT effects occurred in both allogeneic transplant models, even in the absence of histoincompatibilities between donor cells and host tumor (BALB/c[H-2d] --> F1: MethA[H-2d]). Selective inhibition of type-1 (Th-1/Tc1) immune responses with TAK-603 after HSCT nearly abolished GvHD in both allogeneic transplant models. While GvT effects directed against alloantigens (C57BL/6[H-2b] --> F1: MethA[H-2d]) remained unaffected during type-1-immune suppression, GvT effects targeted against tumor-associated antigens (BALB/c[H-2d] --> F1: MethA[H-2d]) were not evident. CONCLUSIONS.: Our data show that GvHD and GvT effects are in principle separable from each other by selective type-1 inhibition in transplantation models with major histocompatibility complex disparities between tumor, host, and donor. In contrast, in situations that only allow for GvT effects that exclusively target tumor-associated antigens (TAAs), type-1 inhibition results in complete abrogation not only of GvHD but also desired GvT reactions. These differences in GvT effects targeting alloantigens or TAAs and their interrelation to GvHD should be considered in future studies aimed at separating GvT reactions from GvHD.

Ex Vivo Soluble Fas Ligand Treatment of Donor Cells to Selectively Reduce Murine Acute Graft Versus Host Disease

BACKGROUND

Allogeneic bone marrow transplantation (BMT) and donor lymphocyte infusion (DLI) provide valuable treatments for a range of diseases. However, the therapeutic utility of BMT and DLI is reduced by the high incidence of graft-versus-host disease (GvHD) mediated by activated donor T lymphocytes directed against recipient alloantigens.

METHODS

Using mouse models, we developed and evaluated a strategy to selectively enhance activation-induced cell death (AICD) of anti-recipient T cells within transplant donor cell populations, with the goal of reducing GvHD. Responder T lymphocytes were incubated ex vivo with irradiated allogenic stimulator cells in a mixed lymphocyte reaction (MLR) in the presence of soluble Fas ligand (sFasL) to induce AICD in alloreactive cells.

RESULTS

This ex vivo sFasL treatment reduced proliferation to the allogeneic stimulator cells in vitro and abrogated acute GvHD capacity in vivo. In contrast, the secondary immune responsiveness of the ex vivo sFasL-treated responder T cells to an unrelated model antigen was preserved. Furthermore, upon adoptive transfer in a DLI model, ex vivo sFasL-treated T cells were able to reject a model tumor. Finally, ex vivo sFasL treatment of bone marrow cells did not reduce their hematopoietic engraftment capacity.

CONCLUSIONS

Thus, ex vivo treatment with sFasL appears to have potential for translation to clinical cell processing of BMT allografts and DLI infusions.

Allogeneic MHC gene transfer enhances antitumor activity of allogeneic hematopoietic stem cell transplantation without exacerbating graft-versus-host disease

Enhancement of the specific antitumor activity of allogeneic hematopoietic stem cell transplantation (alloHSCT) against solid cancers is a major issue in the clinical oncology. In this study, we examined whether intratumoral allogeneic MHC (alloMHC) gene transfer can enhance the recognition of tumor-associated antigens by donor T cells and augment the antitumor activity of alloHSCT. In minor histocompatibility antigen-mismatched alloHSCT (DBA/2-->BALB/c: H-2(d)) recipients, alloMHC gene (H-2K(b)) was transduced directly into a s.c. tumor of CT26 colon cancer cells. Because CT26 cells have an aggressive tumorigenicity in syngeneic BALB/c mice, an H-2K(b) gene transfer provides only a limited antitumor effect after syngeneic (BALB/c-->BALB/c) HSCT. By contrast, the H-2K(b) gene transfer caused significant tumor suppression in the alloHSCT recipients, and this suppression was evident not only in the gene-transduced tumors but also in simultaneously inoculated distant tumors without gene transduction. In vitro cytotoxicity assay showed specific tumor cell lysis by donor T cells responding to the H-2K(b) gene transfer. Graft-versus-host disease was not exacerbated serologically or clinically in the treated mice, demonstrating that alloMHC gene transfer enhances the antitumor effects of alloHSCT without exacerbating graft-versus-host disease. This combination strategy has important implications for the development of therapies for human solid cancers.

Shared biology of GVHD and GVT effects: Potential methods of separation

The difficult separation of clinical graft-versus-tumor (GVT) effects from graft-versus-host disease (GVHD) reflects their shared biology. Experimental approaches to mediate GVT effects while limiting GVHD include: (1) allograft T cell depletion followed by immune enhancement; (2) modulation of T cell dose or T cell subset composition; (3) donor lymphocyte infusion; (4) reduced-intensity host preparation; (5) modulation of Th1/Th2 and Tc1/Tc2 cell balance; (6) cytokine therapy or neutralization; (7) T regulatory cell therapy; (8) co-stimulatory pathway modulation; (9) chemokine pathway modulation; (10) induction of antigen-specific T cells; (11) alloreactive NK cell therapy; and (12) targeted pharmaceutical inhibition of proteosome, mammalian target of rapamycin, and histone deacetylase pathways. Clearly, a multitude of approaches exist that hold promise for separating GVT effects from GVHD. Future success in this endeavor will require a strong commitment towards translational research and continued advances in cell, vaccine, cytokine, monoclonal antibody, and targeted molecular therapy.

G-CSF/SCF reduces inducible arrhythmias in the infarcted heart potentially via increased connexin43 expression and arteriogenesis

Granulocyte colony-stimulating factor (G-CSF), alone or in combination with stem cell factor (SCF), can improve hemodynamic cardiac function after myocardial infarction. Apart from impairing the pump function, myocardial infarction causes an enhanced vulnerability to ventricular arrhythmias. Therefore, we investigated the electrophysiological effects of G-CSF/SCF and the underlying cellular events in a murine infarction model.

G-CSF/SCF improved cardiac output after myocardial infarction. Although G-CSF/SCF led to a twofold increased, potentially proarrhythmic homing of bone marrow (BM)-derived cells to the area of infarction, <1% of these cells adopted a cardial phenotype. Inducibility of ventricular tachycardias during programmed stimulation was reduced 5 wk after G-CSF/SCF treatment. G-CSF/SCF increased cardiomyocyte diameter, arteriogenesis, and expression of connexin43 in the border zone of the infarction. An enhanced expression of the G-CSF receptor demonstrated in cardiomyocytes and other cell types of the infarcted myocardium indicates a sensitization of the heart to direct influences of this cytokine. In addition to paracrine effects potentially caused by the increased homing of BM-derived cells, these might contribute to the therapeutic effects of G-CSF.

Inhibition of tumor growth in immunocompromised hosts by restoring type-2 immunity using infusion of G-CSF-treated allogeneic CD8+ leukocytes

Since recombinant human granulocyte colony-stimulating factor (rhG-CSF)-treated donor leukocyte infusion (G-DLI) has been shown to downregulate type-1 immunity in a heart transplant model, we examined influences of G-DLI on tumor growth in immunosuppressed hosts. F344 rats were treated with tacrolimus (8 mg/kg i.m.) and syngeneic colon adenocarcinoma RCN-9 cells (3 x 10(6)) were inoculated subcutaneously. For G-DLI, allogeneic DA rats were pretreated with rhG-CSF (250 microg/kg, days -5 to 0) and isolated leukocytes or sorted CD8(+) cells were injected intravenously to the hosts on day 0. Tumors in tacrolimus-treated hosts continuously grew over 5 weeks. G-DLI of 100 x 10(6) leukocytes attenuated tumor growth rate while direct host pretreatment with rhG-CSF did not. Notably, G-DLI of 10 x 10(6) CD8(+) cells blocked tumor expansion after day 14. Tacrolimus-induced inhibition of lymphocyte infiltration into tumors was recovered by the G-DLIs. Flow cytometry showed no detectable donor-type T cells in the tumor and circulation. Quantification of intratumor transcription levels using reverse transcription-real-time polymerase chain reaction showed recovery from tacrolimus-induced downregulation of interleukin-4 but not interferon-gamma levels. In vivo rhG-CSF-treated CD8(+) allogeneic cells demonstrate potent anti-tumor effects by restoring type-2 immunity of immunosuppressed hosts.

A crucial role for antigen-presenting cells and alloantigen expression in graft-versus-leukemia responses

Graft-versus-leukemia (GVL) response after allogeneic bone marrow transplantation (BMT) represents one of the most potent forms of immunotherapy against malignant diseases. Antigen-presenting cells (APCs) are crucial for the induction of graft-versus-host disease (GVHD), the most serious complication of allogeneic BMT, but their role in GVL responses is unclear. Using a series of clinically relevant mouse GVL tumor models, we found that APCs and alloantigen expression on tumors are crucial for GVL. Moreover, APCs of host origin predominated in GVL responses although donor APCs contributed as the acuity of tumor burden decreased.

Immunotherapy of cancer through targeting of minor histocompatibility antigens

Minor histocompatibility antigens are allogeneic targets of T-cell mediated graft-versus-tumour effects following allogeneic stem cell transplantation. Recent research has identified several minor histocompatibility antigens as tumour proteins and has also disclosed their unique properties in both the induction and the effector phase of graft-versus-tumour effects. Targeting tumour-specific minor histocompatibility antigens by adoptive immunotherapy will battle against tumour tolerance and evoke allo-immune responses, thereby enhancing graft-versus-tumour effects against leukaemia and solid tumours. Recently acquired knowledge of the role of donor immunisation status, new techniques in the generation of minor histocompatibility antigen-specific cytotoxic T lymphocytes in vitro, and innovative principles in vaccination will help to design clinical trials that exploit minor histocompatibility antigens in the immunotherapy of cancer.